Low scale potential water treatment

ABSTRACT

An electrochemical treating device having low scale potential is disclosed. The device has a variety of configurations directed to the layering of the anionic exchange and cationic exchange. The treatment device can also comprise unevenly sized ion exchange resin beads and/or have at least one compartment that provides a dominating resistance that results in a uniform current distribution throughout the apparatus.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 13/690,866, filed Nov. 30, 2012, titled “LOW SCALEPOTENTIAL WATER TREATMENT,” which is a continuation application of U.S.patent application Ser. No. 11/767,438, filed Jun. 22, 2007, whichclaims the benefit of U.S. Provisional Patent Application Ser. No.60/805,505, filed on Jun. 22, 2006, titled “ENHANCED HARDNESS TOLERANCEOF CEDI MODULES,” U.S. Provisional Patent Application Ser. No.60/805,510, also filed on Jun. 22, 2006, titled “METHODS TO REDUCESCALING IN EDI DEVICES,” and U.S. Provisional Patent Application Ser.No. 60/912,548, filed on Apr. 18, 2007, titled “USE OF INERT RESIN INTHE CONCENTRATE COMPARTMENT TO IMPROVE CURRENT DISTRIBUTION FOR EDIMODULES,” each of which is incorporated herein by reference in theirentirety for all purposes.

BACKGROUND OF INVENTION

1. Field of Invention

This invention relates to systems and methods of water treatment havinga low potential for scale formation and, in particular, to reducing thepotential for scale formation in systems that utilizeelectrically-motivated separation apparatus.

2. Discussion of Related Art

Electrically-motivated separation apparatus including, but not limitedto, electrodialysis as well as electrodeionization devices, have beenused to treat water. For example, Liang et al., in U.S. Pat. No.6,649,037, disclose an electrodeionization apparatus and method forpurifying a fluid by removing the ionizable species.

SUMMARY OF THE INVENTION

One or more aspects of the invention relate to an electrodeionizationapparatus having an anode compartment and a cathode compartment. Theelectrodeionization apparatus comprises a first depleting compartmentdisposed between the anode compartment and the cathode compartment, aconcentrating compartment in ionic communication with the depletingcompartment, a second depleting compartment in ionic communication withthe concentrating compartment, and a first barrier cell in ioniccommunication with and disposed between the first depleting compartmentand at least one of the anode compartment and the cathode compartment.

Other aspects of the invention relate to an electrodeionizationapparatus comprising a depleting compartment and a first concentratingcompartment in ionic communication with the depleting compartment, anddefined at least partially by an anion selective membrane and a cationselective membrane. The first concentrating compartment typicallycontains, at least partially, a first zone comprising substantially ofcation exchange media that is substantially separated from the anionselective membrane by a second zone comprising substantially of anionexchange media.

Still other aspects of the invention relate to an electrodeionizationapparatus comprising a depleting compartment, a first concentratingcompartment in ionic communication with the depleting compartment, and asecond concentrating compartment in ionic communication with thedepleting compartment. The first concentrating compartment typicallycomprises media with a first effective current resistance and the secondconcentrating compartment having a portion thereof comprising media witha second effective current resistance greater than the first effectivecurrent resistance.

Still other aspects of the invention relate to an electrodeionizationapparatus comprising a depleting compartment, and a concentratingcompartment in ionic communication with the depleting compartment. Theconcentrating compartment typically comprises a mixture of anionexchange resin and cation exchange resin and amounts of the anionexchange resin and cation exchange resin in the mixture varies relativeto a flow path length of the concentrating compartment.

Still other aspects of the invention relate to an electrodeionizationapparatus having at least one compartment with at least one outlet portdefined by a distributor having a plurality of apertures. Theelectrodeionization apparatus can comprise a first layer of particles inthe compartment bounded by ion selective membranes. The particles cancomprise media having a first effective diameter less than the smallestdimension of the apertures. The electrodeionization apparatus furthercomprises a second layer of particles in the compartment downstream ofthe first layer. The second layer of particles typically has a secondeffective diameter greater than the first effective diameter and greaterthan the smallest dimension of the apertures.

Still further aspects of the invention relate to electrodeionizationsystem comprising a source of water to be treated, a treating modulecomprising a depleting compartment and a concentrating compartment, thetreating module fluidly connected to the source of water to be treated;an electrolytic module comprising an acid-generating compartment, and asource of a brine solution fluidly connected to an inlet of theacid-generating compartment of the electrolytic module. The electrolyticmodule is fluidly connected upstream of the concentrating compartment.

Aspects of the invention relate to an electrodeionization apparatuscomprising a compartment containing a mixture of anion exchange resinsand cation exchange resins. The anion exchange resins having an averagediameter at least 1.3 times greater than an average diameter of thecation exchange resins.

Aspects of the invention relate to an electrodeionization apparatuscomprising a compartment containing a mixture of anion exchange resinsand cation exchange resins. The cation exchange resins having an averagediameter at least 1.3 times greater than an average diameter of theanion exchange resins.

Still other aspects of the invention relate to a water treatment systemcomprising a source of water to be treated, an electrodeionizationdevice comprising a plurality of concentrating and depletingcompartments and fluidly connected to the source of water to be treated,a chiller in thermal communication with the water to be introduced intoat least one concentrating compartment of the electrodeionizationdevice, a sensor disposed to provide a representation of a temperatureof at least one of water to be introduced into the concentratingcompartment and water exiting the concentrating compartment, and acontroller configured to receive the temperature representation andgenerate a signal that promotes cooling the water to be introduced intothe concentrating compartment.

Still other aspects of the invention relate to electrodeionizationapparatus comprising a depleting compartment at least partially definedby a cation selective membrane and an anion selective membrane, and aconcentrating compartment at least partially defined by the anionselective membrane and containing a first layer of anion exchange mediaand a second layer of media disposed downstream of the first layer, thesecond layer comprising anion exchange media and cation exchange media.

Still other aspects of the invention relate to a method of treatingwater in an electrodeionization device having a depleting compartmentand a concentrating compartment. The method comprising measuring one ofa temperature of a stream in the concentrating compartment, atemperature of a stream to be introduced into the concentratingcompartment, and a temperature of a stream exiting from theconcentrating compartment; reducing the temperature of the water to beintroduced into the concentrating compartment to a predeterminedtemperature; introducing water to be treated into the depletingcompartment; and removing at least a portion of at least one undesirablespecies from the water to be treated in the electrodeionization device.

Still other aspects of the invention relate to a method of treatingwater in an electrodeionization device comprising introducing waterhaving anionic and cationic species into a depleting compartment of theelectrodeionization device, promoting transport of at least a portion ofthe cationic species into a first barrier cell disposed between thedepleting compartment and a cathode compartment of theelectrodeionization device, and promoting transport of at least aportion of the anionic species into a second barrier cell disposedbetween the depleting compartment and an anode compartment of theelectrodeionization device.

Still other aspects of the invention relate to a method of treatingwater in an electrodeionization device having a depleting compartmentand a concentrating compartment. The method comprises introducing waterto be treated into the depleting compartment of the electrodeionizationdevice, promoting transport of an undesirable species from the depletingcompartment into the concentrating compartment of theelectrodeionization device. The concentrating compartment can typicallycontains a first layer of anion exchange media and a second layer ofmedia disposed downstream of the first layer and the second layer cancomprise a mixture of anion exchange media and cation exchange media.

Still other aspects of the invention relate to a method of treatingwater comprising introducing water to be treated into a depletingcompartment of an electrodeionization device, the depleting compartmenthaving at least one layer of ion exchange media; and promoting transportof at least a portion of anionic species from the water introduced intothe depleting compartment from a first layer of ion exchange media intoa first concentrating compartment to produce water having a firstintermediate quality. The first concentrating compartment is defined, atleast partially, by an anion selective membrane and a cation selectivemembrane. The first concentrating compartment contains, at leastpartially, a first zone comprising cation exchange media that issubstantially separated from the anion selective membrane by a secondzone comprising anion exchange media.

Still other aspects of the invention relate to a method of treatingwater in an electrodeionization device. The method comprises introducingwater to be treated comprising undesirable species into a depletingcompartment of the electrodeionization device, promoting transport ofthe undesirable species from the depleting compartment to aconcentrating compartment of the electrodeionization device to producethe treated water; electrolytically generating an acid solution in theancillary module, and introducing at least a portion of the acidsolution into the concentrating compartment.

Further aspects of the invention relate to a water treatment systemcomprising a source of a water to be treated, and an electrodeionizationdevice comprising a first depleting compartment and a second depletingcompartment, each of the first and second depleting compartment fluidlyconnected to the source of water to be treated in a parallel flowconfiguration; and a first concentrating compartment in ioniccommunication with the first depleting compartment and a secondconcentrating compartment fluidly connected to downstream of the firstconcentrating compartment.

Other aspects of the invention relate electrodeionization apparatuscomprising a plurality of depleting compartments configured to haveliquid flowing therein along parallel flow paths, and a plurality ofconcentrating compartments in ionic communication with at least onedepleting compartment, wherein at least portion of the concentratingcompartments are arranged serially.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are not intended to be drawn to scale. In thedrawings, each identical or nearly identical component that isillustrated in various figures is represented by a like numeral. Forpurposes of clarity, not every component may be labeled in everydrawing.

In the drawings:

FIG. 1 is a schematic illustration of a portion of anelectrodeionization apparatus comprising at least one barrier cell inaccordance with one or more embodiments of the invention;

FIG. 2 is a schematic illustration of a portion of anelectrodeionization apparatus having layered beds of media in at leastone concentrating compartment thereof in accordance with one or moreembodiments of the invention;

FIG. 3 is a schematic illustration of a portion of anelectrodeionization apparatus comprising at least one concentratingcompartment having zones of media in accordance with one or moreembodiments of the invention;

FIG. 4 is a schematic illustration of a portion of a treatment system inaccordance with one or more embodiments of the invention;

FIG. 5 is a schematic illustration of a portion of anelectrodeionization apparatus having at least one compartment modifiedto reduce the effective resistance or improve the current distributionin other compartments in accordance with one or more embodiments of theinvention;

FIG. 6 is a schematic illustration of a portion of anelectrodeionization apparatus having a increased effective flow velocityin at least one concentrating compartment thereof in accordance with oneor more embodiments of the invention;

FIGS. 7A and 7B is a schematic illustration of a portion of anelectrodeionization apparatus comprising a compartment containing resinbeads of differing sizes in accordance with one or more embodiments ofthe invention; and

FIG. 8 is a graph showing the relationship between an LangelierSaturation Index value of a water stream relative to the temperature ofthe water stream;

FIGS. 9A and 9B are schematic illustrations of concentrating anddepleting compartment cell pairs in an electrodeionization devicewherein FIG. 9A shows compartments thereof comprising layers of mediaand FIG. 9B shows compartments thereof comprising layers and zones ofmedia in accordance with one or more embodiments of the invention; and

FIG. 10 is a graph showing the performance of electrodeionizationapparatus in accordance with one or more embodiments of the invention.

DETAILED DESCRIPTION

The invention provides electrically-driven separation apparatuses suchas but not limited to filled compartment electrodeionization (CEDI)devices such as those disclosed in U.S. Pat. Nos. 4,632,745, 6,649,037,6,824,662, and 7,083,733, each of which is incorporated herein byreference. In particular, the embodiments implementing one or moreaspects of the invention provide can be, in some cases, characterized ashaving a lower potential or a lower likelihood of forming scale.Although the various aspects of the invention are presented throughembodiments involving electrodeionization devices, such various aspectsof the invention may be practiced in other electrically-driven ormotivated separation apparatus that can facilitate treatment of a fluidhaving at least one undesirable species. Particularly pertinent aspectsof the invention can involve electrodeionization apparatus utilized totreat or remove at least one dissolved species from a water stream or abody of water. Thus, the various aspects of the invention canadvantageously provide electrodeionization apparatuses that areconfigured or operated to treat water having high scale potential.

An aspect of the invention can be implemented in the exemplaryembodiment presented in FIG. 1 which schematically shows a portion of anelectrodeionization apparatus 100. The electrodeionization apparatustypically comprises at least one concentrating compartment 112 and atleast one depleting compartment 114, which constitute a cell pair 115,and disposed in ionic communication with each other and, preferably,between and with an anode compartment 120 and a cathode compartment 122.In an advantageous embodiment of the invention, the electrodeionizationapparatus can further comprise at least one barrier cell 130 that cantrap migrating species. For example, the electrodeionization apparatus100 can have barrier or neutral cells 130 and 132 disposed adjacentanode compartment 120 and cathode compartment 122. Barrier cellstypically provide a buffer for an electrode compartment to separate orprevent species from forming localized scale. Electrodeionizationapparatus typically generate hydroxide ions which can raise the pH atlocalized regions, especially at the points or surfaces conducive toelectrolytic reactions. Such localized regions, or even at the electrodecompartments, typically have pH conditions much greater than the bulk ofthe liquid. Because the barrier cells can serve to isolate such high pHregions from scale-forming species transported from the one or moredepleting compartments during treatment of the water, thereby inhibitingor at least reducing the potential for scale formation. As exemplarilyillustrated in FIG. 1, electrodeionization apparatus 100 can comprisebarrier cell 130 that ionically isolates at least one precipitatablecomponent, such as Ca²⁺, from a component, such as 011, that contributesto scale formation. Typically, one or more of barrier cells 130 can bedefined, at least partially, by an anion selective membrane 140A thatpermits migration of anionic species such as OH⁻ while inhibiting thefurther migration of cationic species into an adjacent compartment. Asillustrated, a barrier cell 130 can be disposed adjacent concentratingcompartment 112. One or more such barrier cells can also further bepartially defined by a cation selective membrane 140C. In this manner,for example, a component of a precipitatable compound, such as Ca²⁺, canbe inhibited from being introduced into a compartment having localizedregions of high pH, such as electrode compartment 120, that typicallyresult from hydroxide species generation.

Other embodiments of the invention can involve barrier cells thatseparate neutral or weakly ionized, or at least ionizable, species, suchas, but not limited to silica, SiO₂. Silica can precipitate from thebulk liquid if the concentration is high enough or where a pH changeoccurs, such as change from a high pH to a neutral pH. Inelectrodeionization apparatus, silica is typically removed while in itsionized state, at high pH. One or more barrier cells 132 can be disposedto ionically isolate an anode compartment 122 of electrodeionizationapparatus 100, wherein hydrogen ions are generated and consequently canhave low or neutral pH liquid flowing therein. After silica migratesfrom depleting compartment 114 into concentrating compartment 112through anion selective membrane 140A, it is trapped by barrier cell 132containing high pH liquid flowing therein and inhibited from furthermigration into the low or neutral pH compartment with neutral or nearneutral pH, and thereby reduce the likelihood of polymerizing intosilica scale. Cell 132, like cell 130, can be defined, at leastpartially, by cation selective membrane 140C and anion selectivemembrane 140A. Barrier cell 132 can thus serve to trap pH-precipitatablespecies and prevent or at least inhibit precipitation of such species.Barrier cell 132 can also contain, at least partially, anion exchangemedia and cation exchange media or a mixture of both. Further, one ormore of the barrier cells can further comprise inert media or otherfiller material that can facilitate assembly of the electrodeionizationapparatus or provide a desirable characteristic such as resistance orflow distribution during, for example, operation of the apparatus.Likewise, one or more of the concentrating compartments, the depletingcompartments, and the electrode compartments can contain, at leastpartially, a mixture of anion and cation exchange media. Indeed, amixture of anion and cation exchange media in the concentratingcompartments and electrode compartments can further reduce scalingpotential by facilitating transport of precipitatable species away fromthe selective membranes which avoids accumulation of an ionic speciesthat may occur in compartments or regions of compartments with a singletype of active exchange media.

In some embodiments of the invention, the anode compartment can contain,at least partially, media that is substantially comprised of oxidationresistant substrate. Thus, for example, durable, highly cross linked ionexchange resin, such as commercially available cation resins, can beused in the anode compartment in which an oxidizing environment may bepresent. Further, cation exchange resin when utilized in the anodecompartment can prevent or inhibit transport of chloride ions to theanode surface where such species may be converted to oxidizing chlorine.

The apparatus of the invention can treat water having hardness ofgreater than 1 mg/L as CaCO₃ or silica content of greater than 1 mg/L,or both. Thus, the apparatus and techniques of the invention are notconfined to conventional operating limits and, when used in a treatmentsystem, can obviate at least one unit operation intended to soften thewater to be treated or remove silica. This advantageously can reducecapital and operating costs while improving the treatment system'sreliability and availability as well as capacity. For example, thetreatment systems of the invention, comprising one or moreelectrodeionization devices described herein, can treat water without atwo-pass reverse osmosis (RO) subsystem, while providing water havingthe same or comparable quality as a system that utilizes a two-pass ROdevice to remove or reduce the concentration of hardness causingcomponents and silica before an electrodeionization device.

Further aspects of the invention can involve electrodeionizationapparatus comprising at least one depleting compartment and/or at leastone concentrating compartment having layered media contained therein.For example, one or more depleting compartments 112 ofelectrodeionization device 100 can comprise a first layer of particles112A, at least a portion thereof comprising active media thatfacilitates transport or migration of a first target, typically ionized,species. Depleting compartment 112 can further comprise a second layer112B comprising, at least partially, active media that facilitatestransport of the first target species and a second target species, orboth. First layer 112A can comprise particles having a first effectivediameter and second layer 112B can have particles with a secondeffective diameter. Further embodiments can involve a third layer 112Cin depleting compartment 112. Third layer 112C can have active or inertmedia, or a mixture of both, with a third effective diameter. Theeffective diameter can be a smallest dimension of a particle.Alternatively, the effective diameter can be an average diameter of thecollective particles and is a calculated diameter of an analogous sphereof comparable volume and surface area. For example, the effectivediameter of particles in a layer can be a function of the ratio of thevolume of a particle to the surface area of a particle or an average ofthe smallest dimension of the particles. In a preferred configuration,the particles in a downstream layer have an effective diameter that isless than the effective diameter of particles in an upstream layer. Forexample, particles comprising layer 112C can be spherical particles witha larger effective diameter than the effective diameter of particlescomprising layer 112B. Optionally, the effective diameter of theparticles comprising layer 112A can be greater than the effectivediameter of particles in layer 112B or 112C. One or more of theconcentrating compartments may be similarly layered.

In a preferred embodiment, the particles in an upstream layer have aneffective diameter that is at least the dimension of interstices betweenthe particles of a downstream layer. In further embodiments, theupstream particles have an effective diameter or a smallest dimensionthat is less than the smallest dimension of the apertures of distributor160 that defines an outlet port of depleting compartment 112.Distributor 160 can be a screen that serves to retain the media withinthe compartments. Thus, each of the depleting compartments andconcentrating compartments containing media can have at least onedistributor that permits fluid flow therethrough while retaining themedia and a layer of media that are sized to retain particles in anupstream layer.

The apertures or openings of distributors are typically designed toretain resins having a diameter of about 500 μm to about 700 μm.Utilizing the configuration of the invention, anion and cation exchangeresins may be utilized having smaller dimensions than the aperturedimensions which improves mass transfer kinetics throughout theapparatus. Further, smaller ion exchange resins can improve packingwithin the compartment and reduces the likelihood of channeling or flowbypass along the compartment walls. Close packed spheres or nearlyspherical particles have interstitial spaces of about 0.414 times theradius of the spheres. Thus, the effective diameter of the upstreamresin is preferably not less than such dimension. For example, the finemesh resin beads having an effective diameter of about 62 μm to about 83μm may be utilized in an upstream layer with a layer of resin beadshaving a diameter of about 300 μm to about 400 μm. Any of the layers maycomprise any suitable fraction of the compartment. The depth of theupstream layer may be dependent on providing a desired performance.Further, advantageous configurations contemplate the use of cation resinbeads having a smaller effective diameter or dimension with larger anionresin beads to facilitate cation migration activity. Notablearrangements are not limited to the use of active resin as the lower,downstream media and the invention may be implemented utilizing inertmedia in one or more of the downstream layers.

The interfaces between the layers may constitute a gradient of small andlarge resin beads. Thus, the boundary between layers need not beparticularly delineated. Other configurations, moreover, can involve amixture of the fine mesh resin beads mixed with larger resins.

Another aspect of the invention can involve electrodeionizationapparatus comprising at least one concentrating compartment havinglayered media contained therein. As illustrated in FIG. 2, theelectrodeionization device 200 can have at least one concentratingcompartment 214 and at least one depleting compartment 212. At least oneof the concentrating compartments 214 can have a first layer 215 and asecond layer 216. In electrodeionization devices that treat relativelypure water, such as RO permeate, the current efficiency is typicallybelow 100% because, it is believed, of water splitting and transport ofthe generated hydrogen and hydroxyl ions. This can create local pHfluctuations and can promote scale formation especially where thehydroxyl species reacts with bicarbonate species or carbon dioxide toform carbonate ions which forms calcium carbonate scale.

For example, in a typical electrodeionization apparatus, bicarbonateions transfer through the anion exchange membrane near the inlet of thecompartment but may be inhibited from migrating further from themembrane. When water splitting occurs, the hydroxyl species transportedthrough the anion exchange membrane can react with the bicarbonatespecies to form carbonate which then reacts with calcium to form calciumcarbonate scale.

By utilizing layers in one or more of the concentrating compartments,target species can be directed to locations where they are less likelyto form scale. As shown in FIG. 2, a layer 215 of anion exchange mediacan be disposed around the inlet of concentrating compartment 214 topromote migration of bicarbonate species. After the bicarbonate speciesis transported through the anion exchange membrane 240A, it is promotedthrough the anion resin of layer 215 and moves towards the cationselective membrane 240C. Even though there are hardness ions passingthrough cation selective membrane 240C, the pH of the fluid isrelatively low around this membrane, which reduces the likelihood offorming carbonate.

The depleting compartments 212 and the other one or more layers 216 ofthe concentrating compartments 214 may contain mixed anion exchange andcation exchange media.

To further reduce or inhibit scale formation, layers of media can bedisposed along a flow path length of the concentrating compartment. Asshown in FIG. 3, one or more concentrating cells may comprise, at leastpartially, a first zone 314A of ion exchange media and a second zone314B of ion exchange media. The first and second zones may be linearlydistributed along the length of the compartment as represented byboundary 350 or may be a gradient of increasing or decreasing amounts oftypes of ion exchange media in zones 315C and 315D and delineated bygradient boundary 351. The first or second zones may comprise, consistessentially of, or consist of anion exchange media, or cation exchangemedia. For example, zone 314A can comprise cation exchange media thatsubstantially segregates zone 314B, which comprises anion exchangemedia, from cation selective membrane 340C. Substantially separatingrefers to, in some cases, being disposed between a zone and a membranesuch that a separating zone comprises or consists essentially of a typeof media, which can be anionic, cationic, or inert.

In some cases, the first zone or second zone can be a mixture ofdiffering amounts of types of ion exchange media. For example, zone 315Ccan comprise, consists essentially of, or consist of cation exchangemedia adjacent cation selective membrane 340C and zone 315D cancomprise, consist essentially of, or consist of anion exchange media,wherein the amount of anion exchange media, relative to the amount ofcation exchange media increases, or decreases, along the flow pathlength or lengthwise dimension, such that a boundary between zones whichis defined by gradient boundary 351. In another embodiment, a third zone(not shown) of media can be disposed between the first and second zones.The third zone can comprise, consists essentially of, or consist ofinert media, cation exchange media, anion exchange media, mixed media,or mixtures thereof. Further, one or more screens can be used betweenzones or within the zones to facilitate filling the compartments of theapparatus, which, during operation can also improve flow distributionand further inhibit scale formation. Assembly and filling can also befacilitated by utilizing a binder to secure the media of each zone. Forexample, media of the first zone can be mixed with a water solublebinder, such as starch. The mixture can then be placed into thecompartment. A second mixture of media of the second zone can besimilarly prepared and disposed in the compartment.

Zone 314B facilitates transport of anionic species, such as bicarbonateions, away from anion selective membrane 340A and zone 315C facilitatestransport of cationic species, such as calcium ions, away from anionselective membrane 340C. Such segregating zones thus reduce thelikelihood of scale formation around membrane surfaces.

As illustrated in FIG. 3, depleting compartment can comprise a firstlayer 312A of media, a second layer 312B of media, and, optionally, athird layer 312C of media. The first layer can comprise a mixture ofanion exchange media, cation exchange media, or inert media. The secondlayer can comprise, consist essentially of, or consist of anion exchangemedia or inert media or a mixture thereof. The third layer can comprise,consist essentially of, or consist of anion exchange media, cationexchange media, inert media, or a mixture thereof.

Further aspects of the invention involve systems and techniques thatmodify the pH of a stream flowing in at least one concentratingcompartment of an electrodeionization apparatus. The pH of the streamcan be reduced to reduce the likelihood of scale formation by generatingand adding an acidic solution to one or more of the concentrate andelectrode compartments. The acidic solution can be generated or preparedby utilizing an electrolytic module. Further scale inhibition ortolerance can be effected by degasification of the concentrate liquid.Any acid generating module may be utilized such as those commerciallyavailable from Dionex Corporation, Sunnyvale, Calif.

Typically, an electrodeionization device can treat liquids having lowhardness. This limitation limits the incoming feed water intoelectrodeionization devices to a hardness level of 1 ppm or less, ascalcium carbonate. To treat water having a hardness value greater than 1ppm, pretreatment processes such as two-pass RO or a softener post RO,must be used. The additional pretreatment unit operations increasesystem complexity and cost as well as waste. The electrodeionizationdevices of the present invention, however, can reliably treat waterhaving higher hardness thereby eliminating or reducing the dependence onsuch pretreatment operations.

Addition of an acidic solution into the concentrating compartment ofelectrodialysis devices to reduce calcium precipitation is known;however adding acidic solutions to electrodeionization devices is notpracticed because of low flow velocity of the streams in the concentratecompartments, especially in thick cell compartment. Further, a highquantity of acid is typically required. As illustrated in FIG. 4, thetreatment system 400 of the invention can comprise an electrochemicaldevice 435 to produce an acid solution to be introduced into acompartment, typically concentrating compartment 414 of anelectrodeionization device 445 disposed to receive water to be treatedfrom source 411. A portion of treated product water fromelectrodeionization device 445 can be used to facilitate generating theacid solution in an acid-generating compartment 472 of electrochemicaldevice 435. At least a portion of the treated water can be delivered toa point of use 413. A source 462 of a brine solution comprising a saltfrom, for example, softener brine tank may be introduced intoelectrolytic module 435 to promote acid solution production.Electrochemical device 435 may be portion of electrodeionization device445. The brine solution typically comprises sodium chloride.

In some cases, the acidic solution can be introduced into one or more ofthe depleting and concentrating compartments 412 and 414, as well as theelectrode compartments of electrodeionization device 445. Preferably,acidic solution is added in an amount to provide a pH of the exitingstream solution leaving the compartment of between about 2.5 to 4.3units. Further embodiments may involve neutralizing one or more streamsfrom electrodeionization device 445. For example a basic solutionproduced from compartment 472 of electrolytic module 435 may be combinedto neutralize an outlet stream, typically having a low pH, fromconcentrating compartment 414 before being discharged to drain 463 orthe environment.

Degasification of the concentrate stream to remove carbon dioxide mayfurther reduce or eliminate the precipitation potential in theconcentrating compartment. Degasification can be accomplished by theaddition of a degasification device or by membrane processes or othermethods. Degasification may be relevant when utilizing an acidicsolution in the concentrating compartment because of the potentialformation of carbon dioxide gas, which can diffuse back through themembrane and reduce product quality. Further, the flow of the streamwithin the compartment may be countercurrent to facilitate gas removal.

Recirculation of the concentrate compartment using a pump and,optionally, a tank can further enhance the scale inhibition by theacidification and degasification techniques described herein.

The components, arrangements, and techniques of the invention alsoprovide improved current distribution in an electrodeionization device.As schematically illustrated in FIG. 5, the current resistance throughthe electrodeionization apparatus 500 between electrodes 520 and 522 canbe characterized by a series of compartment resistances 573, 575, and577, which are representative of the depleting and concentratingcompartments 512 and 514, and by membrane resistances 584, 586, and 588,which are representative of anion selective membranes 540A and cationselective membranes 540B. Improved current distribution throughoutelectrodeionization apparatus 500 can be effected by utilizing at leastone concentrating compartment 516 with at least a portion thereof havingan effective current resistance 580 that is greater than the effectivecurrent resistance of the other compartments, such as the concentratingcompartments.

The effective current resistance of a compartment or portion thereof maybe modified by mixing inert resin beads, or low or non-conductingmaterials, within the concentrating compartment. Selectively increasingthe effective current resistance effects a more uniform currentdistribution through the other compartments. The reduced variations incurrent throughout the depleting compartments, for example, improveoverall performance.

In an electrodeionization device, the electrical resistance may dependon the types of media in the device as well as the active chemical formof those media, i.e., what ions are moving through the media. In alayered bed compartments, the resistance typically vary between thelayers because of the different types of resin and the form of theresins. Typically, the strongly charged species or ions are motivatedand the water splitting phenomena and weak ion promotion follow. Thus,media resins near the inlet of the compartment would exchange with thetarget species in the feed water while media near the outlet would bemostly in the hydrogen and hydroxide forms. Typically, most of thestrongly charged ions must be removed, which may not be effected if thefeed concentration and/or flow are high enough or if the current is lowenough.

If the resistance in the compartments can vary between layers thereof oralong the length of the bed, then the current density can also varyaccordingly. However, the resistance through the entire module may notjust be a function of the resistances of the depleting compartments. Thedepleting compartments are electrically in series with the membranes andthe concentrating compartments and electrode compartments, which may ormay not also vary in resistance along their length. If the resistancesof the depleting compartments are a small portion of the totalresistance through the module, then even if such resistances varysignificantly, the overall resistance will be dominated by other factorsand current distribution will be more uniform. However, if the depletingcompartment resistances are high relative to the other resistances, thecurrent distribution will be affected by resistance differences withinthe depleting compartments.

Typical electrodeionization devices incorporate screen filledconcentrating and/or electrode compartments. In these configurations,the resistance of the water in these compartments is much greater thanthe resistance of the resin in the depleting compartments in most cases,and therefore, current distribution is not generally controlled by theresistances of the depleting compartments. Filling the concentrating andelectrode compartments with resin as well as using lower resistance ionexchange membranes reduces the overall module resistance significantly.However, in certain circumstances this can lead to uneven currentdistribution as the module resistances become dominated by theresistances of the depleting compartments.

In some embodiments of the invention, therefore, screen filledconcentrating and electrode compartments may minimize uneven currentdistribution. However, in most post RO applications, the water has verylow conductivity leading to high module resistance. This high resistancefurther creates limitations if there are electrical potentialconstraints. The invention, in contrast, provides comparable performancewithout using brine injection into the stream flowing into theconcentrating compartment thereby reducing operating cost and processcomplexity.

As noted, mixing inert resin in one or more concentrating and/orelectrode compartment as fillers can increase the resistance in thosecompartments which improves current distribution through the module. Asshown in FIG. 5, one or more concentrating compartment 516 can compriseinert resin to provide higher effective resistance 580 therethroughwhich dominates the collective resistances of other compartments andmembranes. Because the dominant resistance controls the overallresistivity, the effective current distribution through the othercompartments becomes more uniform. The amount of inert resin can bevaried to increase the effective resistance and modify the currentdistribution through the apparatus. Inert resin can also be used inlayers in one or more concentrating and electrode compartments tolocally increase the resistance in certain portions where the diluteresistance is determined to be low. Thus, as shown in FIG. 5, currentdistribution through zone 512 can be matched or made comparable to thecurrent through zone 511 of the apparatus by utilizing a higherresistivity layer in compartment 515 such that the effective resistance573 of the layer of compartment 515 is increased. The amount ofresistance can be effected empirically measuring the effectiveresistance relative to the amount of inert resin utilized.

Other materials with low conductivity, such as polymeric screens orfiber material can be used to increase the resistance along with theinert resin beads.

Electrodeionization apparatus may be limited to a maximum recovery of90-95% to prevent scale formation of limited solubility species in thefeed water such as hardness and silica. If the feed water contains verylow amounts of these species the device should be able to operate athigher recovery rates. Some aspects of the invention involveelectrodeionization apparatus having multiple passes throughconcentrating compartments thereof thereby providing recovery rates. Themultiple pass configurations facilitate maintaining a predeterminedvelocity without a recirculation pump and loop. However, this inventionis may be preferably utilized in applications with recirculating loopswherein the feed water ion concentration is low and a very high recoveryis desired to avoid wasting or discharging high purity water and/orincreasing operating time of the makeup system. In some embodiments ofthe electrodeionization apparatus of the invention, the fluid flow rateis sufficient to reduce the likelihood of creating dead volumes,channeling and localized overheating within the compartments. Forexample, the desired fluid flow rate in a compartment can be at leastabout 2 gallons per minute per square foot in a concentratingcompartment. Other fluid flow rates may be dictated by other factorsincluding, but not limited to, the concentration of a component of theprecipitating compound, the temperature of the fluid, and the pH of thefluid. Lower velocities may induce channeling.

FIG. 6 schematically illustrates a portion of an electrodeionizationapparatus 600 comprising depleting compartments 614 and concentratingcompartments 612 between electrode compartments 630 and 632. Thearrangement and configuration provide one depleting compartment passwith an associated plurality of concentrating compartment passes in thetreatment apparatus and systems of the invention. Such configurationsallow for an increased fluid flow velocity in the concentratingcompartments, preferably up to five times greater than the flow rate ofa single pass device. As shown in FIG. 6, water from source 615 issequentially introduced into concentrating compartments 612 and directedinto downstream concentrating compartments 612B and then to compartments612C and to drain or to downstream unit operation 625.

Water to be treated is introduced into depleting compartments 614 anddirected to point of use without following or tracking the flow of waterthrough compartments 612, 612A, and 612B. The invention, however, is notlimited to the number of associated concentrating compartment volumesrelative to the number of depleting compartment volumes and any ratio ofconcentrating compartments to depleting compartments can be used toprovide a desired high fluid flow rate through the compartments.

Different size cation and anion exchange resin beads in the mixed layersor compartment may be utilized to further reduce the transport rate ofthe larger bead counter-ions and facilitate transport of the smallerbead counter-ions.

Ion transport typically occurs through the ion exchange resins.Successful transport may thus depend on a complete path of like materialbetween the beads and the membranes. A cationic species typicallydiffuses onto a cation resin bead and will tend to move toward thecathode following a path of cationic media until it reaches the cationselective membrane and passes through into the concentratingcompartment. If the path is broken, the cationic species will have todiffuse out of the last bead and into the bulk solution, thereforereducing the chance it will be picked up later in the bed and increasingthe chance it will end up in the product water. The path can be brokenby poor packing such that the beads don't have good contact or it can bebroken by a bead of the opposite charge.

Using a relatively thin cell or tightly packing the resins can increasethe probability of maintaining the desired pathway. Utilizing cation andanion exchange resin of a similar and relatively uniform size will alsoincrease the likelihood of maintaining the desired pathway. Using cationand anion exchange resin of different sizes, however, can blocktransfer.

In some cases, it may be advantageous to inhibit transport of eithercations or anions. By selectively reducing the size of one type of resinin a mixed bed, the transfer of the smaller bead counter-ions will beenhanced due to more complete paths whereas the transfer of the largerbead counter-ions will be retarded due to fewer complete paths becauseas the size of the smaller beads approaches some fraction of the size ofthe larger beads, smaller resin beads tend to pack around the largerbeads, which isolates and breaks the path from one large bead to thenext. This phenomenon may also depend on the relative ratio of the largeand small ion exchange resin beads. For example a mix of 50% small beadsby volume would affect the transport of ions much differently than a mixof 25% or 75% small beads by volume.

Once the size and mix ratios of the media are appropriately selected toslow transport of a target or selected type of ion and increasetransport of different type, hydrogen or hydroxyl ions must betransferred to maintain electro neutrality. For example, if a bedconsisting essentially of cation resin is used in a depletingcompartment as shown in FIG. 7A, cationic species would migrate throughthe cation exchange resin beads 731 and the cation membrane 740C into anadjacent concentrating compartment. Water would split at site 766 of theanion selective membrane 740A which creates a hydrogen ion that replacesthe migrating cation in the depleting compartment and a hydroxyl ionwhich migrates into an adjacent concentrating compartment whichneutralizes the cationic species migrating from another depletingcompartment (not shown). This phenomenon relies on the ability to splitwater on the surface of the anion membrane where there is relativelylittle contact area between the anion membrane and cation beads.Utilizing smaller cationic exchange resin beads 733 with larger anionicexchange resin beads 734, as illustrated in FIG. 7B, reduces thetransport rate of anionic species. Further, the use of differing resinbead sizes provides additional water splitting sites 766 at the tangentsbetween the cation exchange resin 733 and anion exchange resins beads734, which in turn improves performance by reducing the resistanceacross the module.

For example, an electrodeionization apparatus of the invention cancomprise a compartment containing a mixture of anion exchange resins andcation exchange resins, the cation exchange resins having an averagediameter at least 1.3 times greater than an average diameter of theanion exchange resins. Alternatively or in addition, theelectrodeionization apparatus can comprise a compartment containing amixture of anion exchange resins and cation exchange resins, the cationexchange resins having an average diameter at least 1.3 times greaterthan an average diameter of the anion exchange resins.

EXAMPLES

The function and advantages of these and other embodiments of theinvention can be further understood from the examples below, whichillustrate the benefits and/or advantages of the one or more systems andtechniques of the invention but do not exemplify the full scope of theinvention.

Example 1

This example describes the effect of temperature on the LangelierSaturation Index (LSI).

Calculating an LSI value is known in the art for a measure of thepotential for scale formation. LSI is a function of pH, total dissolvedsolids (TDS), temperature, total hardness (TH), and alkalinity. Usingthe following estimates for these parameters for a concentratingcompartment stream of an electrodeionization apparatus, the temperatureof the stream relative to the LSI value can be defined and arepresentative relationship is shown in FIG. 8, based on a stream with apH of 9.5 units, TDS of 30 ppm, TH of 15 ppm, as CaCO₃, and analkalinity of about 25 ppm, as CaCO₃.

When the LSI value of a stream, is positive scaling is likely to occur.To inhibit scaling, the LSI value of the stream is reduced to,preferably a negative quantity. FIG. 8 shows that as the temperature isreduced the LSI value is reduced to below zero around 12.5° C. Thus, forthe conditions described above, cooling the stream into theconcentrating compartment of an electrodeionization device to below12.5° C. should reduce the likelihood or prevent the formation of scale.

Cooling can be effected by thermally coupling a heat exchanger, orchiller, upstream of the electrodeionization apparatus. Other componentsand subsystems that facilitate removing thermal energy from the one ormore streams into the apparatus may be utilized. For example, one ormore sensors and controllers may be utilized to define a temperaturecontrol loop and facilitate maintaining the temperature of the stream toa target temperature or even to reduce the effective LSI value to adesired or target amount.

The target temperature can be determined empirically, by defining atemperature of the stream to be introduced into a concentratingcompartment of the electrodeionization device, or be calculated based atleast partially on the calculated LSI value. For example, an empiricallyestablished target temperature can be a temperature at which no scalingis historically observed with or without an additional margin to ensurethat the scaling is further inhibited. An LSI-based target temperaturemay be defined based on a derived LSI-temperature relationship thencalculating the target temperature associated with a set reduction inLSI value.

Example 2

In this example, the effect of resin bead size on the performance of anelectrodeionization apparatus in accordance with one or more aspects ofthe invention was studied.

In one test, an electrodeionization module was constructed using anequal mixture of anion resin with an average bead diameter of 575 μm anda cation resin with an average bead diameter of 350 μm in the depletingcompartments. Both of these resins were uniform particle size accordingto industry standards.

The module was fed a water that was previously treated by reverseosmosis and contained about 0.5 ppm Mg and 1.5 ppm Ca (both as CaCO₃)with a pH of about 6.1. The module was operated at almost 100% currentefficiency and product quality was about 1-2 Ω-cm without almost zerosilica removal.

The product water hardness level was below detection as measured by aHach spectrophotometer (<10 ppb) and the pH was reduced to about 5.7.This indicates that the module was preferentially removing cations overanions.

Example 3

In this example, the effect on the performance of an electrodeionizationapparatus with several layers of different bead sizes in compartmentsthereof in accordance with one or more aspects of the invention, wasstudied.

A module was constructed with three layers of ion exchange resin in thedepleting compartments. The first and last layers consisted of an evenmix of cation and anion resin of uniform particle diametersapproximately 600 μm. The middle layer consisted of an even mix ofcation exchange and anion exchange resins with particle diameters of150-300 μm. The module spacer had slots in the flow distributor, whichare used to hold resins in place, with a width of 254 μm. The module wasoperated for several months with no change in pressure drop, whichindicates that the resins in the middle layer, of which some weresmaller than the spacer apertures, did not pass through the bottom layerof resin and exit the module.

In addition, the addition of the middle layer of smaller resins improvedthe performance of a comparable electrodeionization device, controlmodule. The module was operated in parallel with anotherelectrodeionization module having compartments containing an even mix ofcation exchange and anion exchange resins with particle diameters ofabout 600 μm. With a feed water previously treated by reverse osmosishaving a conductivity of about 30 μS/cm and containing 3.75 ppm of CO₂,the module comprising a layer of smaller ion exchange resins producedwater having a resistivity of 16.4 MΩ-cm whereas the other typicalmodule, without a layer of smaller ion exchange resins, produced waterhaving a resistivity of 13.5 MΩ-cm. Further, the module comprising thelayer of smaller exchange resins showed a silica removal of 96.6% versus93.2% for the control module.

Example 4

In this example, the effect on the performance of an electrodeionizationapparatus with several or multiple passes through concentratingcompartments thereof was studied.

An electrodeionization module was assembled with four depletingcompartments, three concentrating compartments, and two electrodecompartments. All of the depleting compartments were fed a water to betreated in to parallel to each other.

The concentrating compartment and electrode compartments were fed inseries so that the stream introduced into the concentrating compartmentsentered the cathode compartment first, then flowed sequentially throughthe concentrating compartments and finally through the anodecompartment. This contrasts with the conventional configuration in whicha water stream is typically fed into the electrode compartments inparallel with a water stream into the concentrating compartments. Themodule thus had five effective concentrating compartment passes.

Data for this module (labeled as “Series Concentrate”) along withperformance data for a standard module operating with parallel flows(labeled as “Parallel Concentrate”) is listed in Table 1 below. The datashow that by serially arranging the stream to flow through theconcentrating and electrode compartments, a fluid flow velocity similarto that when operating in parallel at a much lower reject flow rate.Therefore very high recoveries can be obtained while maintaining aminimum velocity in the concentrate.

TABLE 1 Comparison of module with single pass concentrate versus modulewith five passes. Module Parallel Concentrate Series Concentrate Feed,μS/cm 30.3 30.3 Electrical resistance, Ohms 4.3 4.2 Product quality,MΩ-cm 3.1 3.6 Product flow, gpm 2.25 2.25 Concentrate flow, gph 7.2 1.2Recovery, % 94.9 99.1 Concentrate velocity, gpm/ft² 2.0 1.7

Example 5

In this example, the effect on the performance of an electrodeionizationapparatus with horizontal and vertical layers in the concentratingcompartment was studied.

Two modules were assembled with different layering configurations asshown in FIGS. 9A and 9B. Each module was comprised of four of of therespectively illustrated repeating cell pairs. In the figures, “MB”refers to a mixture or resins; “A” and “C” refer to zones or layerscomprising anion exchange resin and cation exchange resin, respectively;and “AEM” and “CEM” refer to the anion selective membrane and cationselective membrane. The modules were operated for two and three weeksrespectively with feed water having a conductivity of about 10 μS/cm andcontaining 2 ppm total hardness, as calcium carbonate.

After this period they were opened and no scale was observed. Incontrast, a non-layered module containing mixed bed resin in thedepleting and concentrating compartments showed scale on the anionmembranes in the concentrate after two weeks of operation on the samefeed water.

Example 6

In this example, the effect on the performance of an electrodeionizationapparatus with vertical layers in compartments thereof along withaddition of an acidic solution, was studied.

Three modules were assembled with horizontal layering in the depletingcompartment and vertically oriented zones or layers, along the flow pathlength, in the concentrating compartments. Barrier cells were alsodisposed adjacent both electrode compartments. The modules were operatedfor ninety days with post-RO feed water containing about 2 ppm of totalhardness. An acidic solution was injected into the concentratingcompartments at rate that provide a pH of the water stream exiting theconcentrating compartments of about 2.5-3.5.

FIG. 10 shows stable performance over the entire ninety days. In thefigure, “FCE” refers to feed conductivity equivalent, which iscalculated by adding the actual feed conductivity, in μS/cm, to the feedcarbon dioxide, in ppm, times 2.67 and the feed silica, in ppm times,1.94; and “Feed TH” refers to feed total hardness.

The controller of the system of the invention may be implemented usingone or more computer systems. The computer system may be, for example, ageneral-purpose computer such as those based on an Intel PENTIUM®-typeprocessor, a Motorola PowerPC® processor, a Sun UltraSPARC® processor, aHewlett-Packard PA-RISC® processor, or any other type of processor orcombinations thereof. Alternatively, the computer system may includespecially-programmed, special-purpose hardware, for example, anapplication-specific integrated circuit (ASIC) or controllers intendedfor analytical systems.

The computer system can include one or more processors typicallyconnected to one or more memory devices, which can comprise, forexample, any one or more of a disk drive memory, a flash memory device,a RAM memory device, or other device for storing data. The memory istypically used for storing programs and data during operation of thetreatment system and/or computer system. Software, including programmingcode that implements embodiments of the invention, can be stored on acomputer readable and/or writeable nonvolatile recording medium, andthen typically copied into memory wherein it can then be executed by theprocessor. Components of the computer system may be coupled by aninterconnection mechanism, which may include one or more busses (e.g.,between components that are integrated within a same device) and/or anetwork (e.g., between components that reside on separate discretedevices). The interconnection mechanism typically enables communications(e.g., data, instructions) to be exchanged between components of thecomputer system. The computer system can also include one or more inputdevices, for example, a keyboard, mouse, trackball, microphone, touchscreen, and one or more output devices, for example, a printing device,display screen, or speaker. In addition, the computer system may containone or more interfaces that can connect the computer system to acommunication network (in addition or as an alternative to the networkthat may be formed by one or more of the components of the computersystem).

According to one or more embodiments of the invention, the one or moreinput devices may include sensors for measuring parameters.Alternatively, the sensors, the metering valves and/or pumps, or all ofthese components may be connected to a communication network that isoperatively coupled to the computer system. The controller can includeone or more computer storage media such as readable and/or writeablenonvolatile recording medium in which signals can be stored that definea program to be executed by one or more processors. Storage medium may,for example, be a disk or flash memory. Although the computer system maybe one type of computer system upon which various aspects of theinvention may be practiced, it should be appreciated that the inventionis not limited to being implemented in software, or on the computersystem as exemplarily shown. Indeed, rather than implemented on, forexample, a general purpose computer system, the controller, orcomponents or subsections thereof, may alternatively be implemented as adedicated system or as a dedicated programmable logic controller (PLC)or in a distributed control system. Further, it should be appreciatedthat one or more features or aspects of the invention may be implementedin software, hardware or firmware, or any combination thereof. Forexample, one or more segments of an algorithm executable by thecontroller can be performed in separate computers, which in turn, can becommunication through one or more networks.

Those skilled in the art should appreciate that the parameters andconfigurations described herein are exemplary and that actual parametersand/or configurations will depend on the specific application in whichthe systems and techniques of the invention are used. Those skilled inthe art should also recognize or be able to ascertain, using no morethan routine experimentation, equivalents to the specific embodiments ofthe invention. It is therefore to be understood that the embodimentsdescribed herein are presented by way of example only and that, withinthe scope of the appended claims and equivalents thereto; the inventionmay be practiced otherwise than as specifically described.

Moreover, it should also be appreciated that the invention is directedto each feature, system, subsystem, or technique described herein andany combination of two or more features, systems, subsystems, ortechniques described herein and any combination of two or more features,systems, subsystems, and/or methods, if such features, systems,subsystems, and techniques are not mutually inconsistent, is consideredto be within the scope of the invention as embodied in the claims.Further, acts, elements, and features discussed only in connection withone embodiment are not intended to be excluded from a similar role inother embodiments.

As used herein, the term “plurality” refers to two or more items orcomponents. The terms “comprising,” “including,” “carrying,” “having,”“containing,” and “involving,” whether in the written description or theclaims and the like, are open-ended terms, i.e., to mean “including butnot limited to.” Thus, the use of such terms is meant to encompass theitems listed thereafter, and equivalents thereof, as well as additionalitems. Only the transitional phrases “consisting of” and “consistingessentially of,” are closed or semi-closed transitional phrases,respectively, with respect to the claims. Use of ordinal terms such as“first,” “second,” “third,” and the like in the claims to modify a claimelement does not by itself connote any priority, precedence, or order ofone claim element over another or the temporal order in which acts of amethod are performed, but are used merely as labels to distinguish oneclaim element having a certain name from another element having a samename (but for use of the ordinal term) to distinguish the claimelements.

U.S. Provisional Patent Application Ser. No. 60/805,505, filed on Jun.22, 2006, titled ENHANCED HARDNESS TOLERANCE OF CEDI MODULES, and U.S.Provisional Patent Application Ser. No. 60/805,510, filed on Jun. 22,2006, titled METHODS TO REDUCE SCALING IN EDI DEVICES, are incorporatedherein by reference.

What is claimed is: 1-24. (canceled)
 25. An electrodeionizationapparatus having at least one compartment with at least one outlet portdefined by a distributor having a plurality of apertures, comprising: afirst layer of particles in the compartment bounded by ion selectivemembranes, the particles comprising media having a first effectivediameter less than the smallest dimension of the apertures; and a secondlayer of particles in the compartment downstream of the first layer, thesecond layer of particles having a second effective diameter greaterthan the first effective diameter and greater than the smallestdimension of the apertures.
 26. The electrodeionization apparatus ofclaim 25, further comprising a third layer of particles disposedupstream of the first layer of particles.
 27. The electrodeionizationapparatus of claim 26, wherein the third layer comprises particleshaving about the same effective diameter as the particles of the secondlayer.
 28. The electrodeionization apparatus of claim 25, wherein thesecond layer comprises ion exchange resin.
 29. The electrodeionizationapparatus of claim 25, wherein the first layer comprises an ion exchangeresin.
 30. The electrodeionization apparatus of claim 25, wherein thethird layer comprises ion exchange resin. 31-64. (canceled)
 65. Theelectrodeionization apparatus of claim 25, wherein the first layer ofparticles has an effective diameter that is at least the dimension ofthe interstices between the second layer of particles.
 66. Theelectrodeionization apparatus of claim 26, wherein the second layer ofparticles has an effective diameter that is at least the dimension ofthe interstices between the third layer of particles.
 67. Theelectrodeionization apparatus of claim 25, wherein the first layer ofparticles has at least one of an effective diameter and a smallestdimension that is less than the smallest dimension of the apertures ofthe distributor.
 68. The electrodeionization apparatus of claim 26,wherein the second layer of particles has at least one of an effectivediameter or a smallest dimension that is less than the smallestdimension of the apertures of the distributor.
 69. Theelectrodeionization apparatus of claim 26, wherein at least one of thefirst layer of particles, the second layer of particles, and the thirdlayer of particles comprises close packed spheres.
 70. Theelectrodeionization apparatus of claim 69, wherein the close packedspheres have interstitial spaces of about 0.4 times the radius of thespheres.